1. Field of the Invention
The present invention relates generally to apparatus and methods for servicing a well, and more particularly, to apparatus and methods for the early evaluation of a well after the borehole has been partially drilled and before casing has been cemented in the borehole such that testing of the well and further drilling may be carried out on a single trip of the tool into the well.
2. Description of the Prior Art
During the drilling and completion of oil and gas wells, it is often necessary to test or evaluate the production capabilities of the well. This is typically done by isolating a subsurface formation or a portion of a zone of interest which is to be tested and subsequently flowing a sample of well fluid either into a sample chamber or up through a tubing string to the surface. Various data, such as pressure and temperature of the produced well fluids, may be monitored downhole to evaluate the long-term production characteristics of the formation.
One commonly used well testing procedure is to first cement a casing in the wellbore and then to perforate the casing adjacent the formation or zone of interest. Subsequently, the well is flow-tested through the perforations. Such flow tests are commonly carried out with a drill stem test string located within the casing. The drill stem test string carries packers, tester valves, circulating valves and the like to control the flow of fluids through the drill stem test string.
Although drill stem testing of cased wells provides very good test data, it has the disadvantage that the well must first be cased before the test can be conducted. Also, better reservoir data can often be obtained immediately after the well is drilled and before the formation has been severely damaged by drilling fluids and the like.
For these reasons, it is often desired to evaluate the potential production capability of a well without incurring the cost and delay of casing the well. This has led to a number of attempts at developing a successful open-hole test which can be conducted in an uncased borehole.
One approach which as been used for open-hole testing is the use of a weight-set, open-hole compression packer on a drill stem test string. To operate a weight-set, open-hole compression packer, a solid surface must be provided against which the weight can be set. Historically, this is accomplished by a perforated anchor which sets down on the bottom. Prior to such drill stem testing, it is necessary to remove the drill string from the well and then run the test string into the well. Afterwards, if it is desired to further drill the well, the test string must be removed so that the drill string may be run back into the well for the additional drilling procedure.
Thus, there is a need for reducing the number of trips in and out of the well which reduces both the cost of testing and drilling and also allows the testing to be conducted at an early stage before significant damage is done to the formation or zone of interest. The present invention meets these needs by providing a testing system which allows an open-hole test to be carried out and then additional drilling to be done on the same trip into the well.
The present invention includes a well testing system and method of testing and drilling a well. Specifically, the apparatus is referred to as a test, drill and pull tool. This apparatus is adapted for use on a tool or drill string for testing in an uncased wellbore.
The apparatus comprises a packer having a set position for sealing engagement with the wellbore and packer and an unset position for disengagement from the wellbore, a tester valve in communication with the drill string and having an open position such that fluid from the well will flow into the drill string during a well test when the packer is set and further having a closed position, and a drill bit adapted for further drilling of the well after the packer lockout has been engaged. The packer is preferably a compression or squeeze packer which is set by setting down weight on the drill string and unset by picking up the drill string, the packer being resettable in this way without removal from the wellbore.
The apparatus may also comprise a packer lockout having an engaged position which prevents resetting of the packer when weight is set down on the drill string and packer after the packer has been set and subsequently unset. The packer lockout is preferably engaged by rotation of the drill string. When this packer lockout is engaged, the drill bit may be rotated. In one embodiment, the drill bit may be rotated by rotating the drill string, and in another embodiment, the drill bit may be rotated by a mud motor actuated by pumping mud down the drill pipe.
The tester valve may be a surface readout tester valve, and the apparatus may further comprise a valve probe latchably engagable with the tester valve. In the illustrated embodiment, the valve probe is connectable to a wireline on which the valve probe may be run into the wellbore and engaged with the tester valve. Pulling on the wireline will open the tester valve for the test, and slacking off on the wireline will close the tester valve. The valve probe may further comprise a sampler adapted for trapping a fluid sample during the well test and/or a flow meter or xe2x80x9cspinnerxe2x80x9d for determining fluid flow rates therethrough during the well test.
The setting and unsetting of the packer and the testing of the well with a tester valve may be carried out any number of times as desired prior to actuation of the packer lockout.
The apparatus may also comprise an isolation valve in communication with the drill string and having a closed position for testing the well and an open position wherein the drill string is placed in communication with the well during a drilling operation. The isolation valve may be actuated by rotation of the drill string, or alternatively, the isolation valve may be configured such that it is pressure actuated.
The apparatus additionally comprises a perforated anchor between the packer and drill bit. The perforated anchor is in communication with the tester valve, and fluid may flow through the perforated anchor into the drill string during a well test. A check valve is provided in the anchor and adapted for allowing fluid to enter the drill string during the well test and preventing discharge of fluid from the anchor during a drilling operation with the drill bit.
Stated in another way, the apparatus of the present invention is adapted for use on a drill string in an uncased wellbore and comprises a packer having a set position for sealing engagement with the wellbore and an unset position disengaged from the wellbore, a tester valve in communication with the drill string and having an open position and a closed position, a valve probe connectable to the tester valve for actuating the tester valve between the open and closed positions thereof, and a drill bit adapted for further drilling of the wellbore. The packer is adapted such that, after a selected cycle of setting and unsetting of the packer, it cannot be reset, and the drill bit is adapted for further drilling after the selected cycle of setting and unsetting the packer. The prevention of resetting of the packer is preferably accomplished by a packer lockout which prevents resetting of the packer after the selected cycle of setting and unsetting the packer.
The invention also includes a method of testing and drilling a well which comprises the step of running a tool string into the well and positioning the tool string adjacent to a bottom portion of the well. This tool string comprises a length of drill pipe, a packer connected to the drill pipe, a tester valve, and a drill bit. The method further comprises the steps of setting the packer into sealing engagement with an uncased borehole of the well, opening the tester valve so that the fluid will flow from a formation or zone of interest into the tool string, closing the tester valve, locking the packer such that it cannot be reset, unsetting the packer, drilling the well deeper with the drill bit.
The step of opening the tester valve may comprise flowing fluid into the drill pipe and flowing at least a sample portion of the fluid through the drill pipe to the surface of the well.
After the step of closing the tester valve, and before the step of locking the packer, the method may further comprise repeating the steps of opening the tester valve and closing the tester valve as many times as desired. After the step of closing the tester valve, and before the step of locking the packer, the method may also comprise unsetting the packer and repeating the steps of setting the packer, opening the tester valve and closing the tester valve as many times as desired. The method may further comprise running the tool string out of the well, unlocking the packer, and repeating the previously mentioned steps.
The step of locking the packer may comprise actuating a packer lockout in the tool string, and in the preferred embodiment, this step is carried out by rotating the tool string.
The method of testing and drilling a well may further comprise the steps of running a valve probe into the drill string on a wireline, and latching the valve probe to the tester valve. The step of opening the tester valve comprises applying tension to the wireline, and the step of closing the tester valve comprises slacking off on the wireline.
During the step of drilling, fluid is pumped down the tool string while preventing flow of fluid from the well into the tool string. Drilling may be accomplished by rotating the tool string or pumping the fluid through a mud motor connected to the drill bit.
Additionally, the method may comprise trapping a fluid sample while fluid is flowing from the formation or zone of interest and/or measuring a flow rate of the fluid flowing from the formation or zone of interest.
Numerous objects and advantages of the invention will become apparent as the following description of the preferred embodiment is read in conjunction with the drawings which illustrate such embodiment.